= K3 intersection lattice
{c}
{title2=$H^2(\mathrm{K3},\mathbb Z)\cong3U\oplus2E_8(-1)$}
The <cup product> on the second integral <cohomology> of a complex <K3 surface> is an <even unimodular lattice> of signature $(3,19)$. Here $U$ is the <hyperbolic plane (quadratic form)> and $E_8(-1)$ is the negative-definite form of the <E8 lattice>. In the <M-theory K3 duality>, this lattice matches the heterotic electric charge lattice. The self-dual harmonic two-forms of a <Ricci flat> K3 metric span its positive three-plane.
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